Riala, Hakko, Isohanni, Räsänen — Department of Psychiatry; Pouta — Department of Public Health Science and General
Practice and Department of Obstetrics and Gynecology, University of Oulu, Finland.

Abstract

Objective: Although the association between smoking and schizophrenia is well known, little attention has been paid to the time between initiation of smoking and onset of schizophrenia. Our goal was to study this putative temporal relation among patients with schizophrenia.

Methods: We used data from the Northern Finland 1966 Birth Cohort (n = 11 017) linked with the National Finnish Hospital Discharge Register to study age at initiation of smoking and age at onset of schizophrenia, and we examined associations between family and environmental factors and the retrospectively determined regular smoking among patients with schizophrenia.

Results: Our main finding was that the initiation of regular smoking was closely related to the onset of schizophrenia. The mean difference in time between the initiation of regular smoking and the onset of schizophrenia among patients (n = 30) was 2.3 (standard deviation [SD] 6.6) years, which was statistically significantly lower than that for subjects with other psychoses (n = 18) (8.6 [SD 6.3] yr) (p < 0.001). Among patients with schizophrenia, the increased likelihood of smoking was associated only with paternal smoking in the family environment, but not with any other background factors (odds ratio 3.5, 95% confidence interval 1.9–11.3).
Conclusion: Smoking may be a sign of the prodromal phase of schizophrenia.

Acknowledgements: We wish to thank the Finnish Academy, the Finnish Psychiatric Research Foundation, the Sigrid Juselius Foundation, the Stanley Medical Research Institute, the Emil Aaltonen Foundation
and the Juho Vainio Foundation for their financial support.